1. Field of the Invention
The present invention relates to a defect inspection method and a defect inspection equipment for inspecting pattern defects and so on in use of an image pick-up device in manufacturing processes and so on of semiconductor devices, in particular, to a method and an equipment for improving detectivity in a case that a surface of a conductor pattern, formed as a film, is extremely rough.
2. Discussion of Background
In a manufacturing process of semiconductor devices, a short-circuit and a hiatus of conductor patterns occur at a time of forming a film and of etching, and reaction byproducts and so on are deposited as extraneous matters, whereby failures of the semiconductor devices occur. In a conventional technique, a defect inspection equipment of an image comparison type, using a white light or a laser beam, is widely used as an equipment effective for inspecting these failures in processes such as film formation and etching. FIG. 12 illustrates a structure of a conventional inspection equipment disclosed in Japanese Unexamined Patent Publication JP-A-60-202949. In the figure, numerical reference 21 designates a wafer to be inspected; numerical reference 22 designates a movable stage; numerical reference 23 designates a light source; numerical reference 24a designates an inspection light; numerical reference 24b designates a reflection light; numerical reference 25 designates an aperture diaphragm; numerical reference 26 designates a half-silvered mirror; numerical reference 27 designates an objective lens; numerical reference 28 designates a mirror; numerical reference 29 designates a camera; numerical reference 30 designates an image pick-up device; numerical reference 31 designates an image processing computer; numerical reference 32 designates an image memory; numerical reference 33 designates a monitor; numerical reference 40 designates a defective address storing unit; and numerical reference 41 designates a determination output unit.
In thus constructed conventional defect inspection equipment, the wafer 21, on which a conductor pattern and so on are formed is located on a movable stage 22, and lighted by the light source 23 in order to manufacture a device. The light emitted from the light source 23 is adjusted by the aperture diaphragm to be an appropriate light volume so as to be the inspection light 24a. The inspection light 24a is turned in a direction of the wafer 21 by the half-silvered mirror 26, converged by the objective lens 27, and introduced into the wafer 21. The reflection light 24b corresponding to various matters on the wafer 21 is enlarged by the objective lens 27, and introduced into the image pick-up device 30, which is integrated in the camera 29, through the half-silvered mirror 26 and the mirror 28. An optical image expressed by intensity of the reflection light 24b is transformed to electric charges by the image pick-up device, and taken out as an electric pixel signal. This electric pixel signal is processed as a picture element pixel signal by the image processing computer 31. The picture pixel signal is compared with reference data, which is previously picked in a similar manner thereto and stored in the image memory 32, and thereafter a defect is judged. An address subjected to the defect determination is stored in the defective address storing unit 40, and the determination is outputted to the determination output unit 41, whereby it is possible to know a position of the defect. Further, it is possible to visually inspect the image by the monitor 33.
In the conventional inspection method in use of the conventional inspection equipment, an inspector ordinarily watches the monitor so that a contrast of an entire inspection image is clear by adjusting the aperture diaphragm 25 to determine appropriate lighting conditions, whereby the image can be recognized. In this case, when a gray image is used, e.g. no pixel signal (darkest) is represented by 0 and saturation of pixel signal (brightest) is represented by 100, an appropriate range is wide enough to be 10 through 90. The optical image taken in the image pick-up device is transformed to the pixel signal within this range. For example, pixel signals of various materials included in an area A of the inspection image data, illustrated in FIG. 13, correspond to values in proportional to illumination reflectances of the materials, wherein a conductor pattern 34 is 80; an oxide film 38 is 25; a short-circuit 35 of the conductor pattern is 80; a hiatus 36 is 25; a deposited conductive extraneous matter 37 is about 60. Pixel signals of a conductor pattern in an area (not shown) similar to that in the reference image data without defects and of an oxide film are respectively about 80 and 25. Accordingly, absolute values of pixel signal differences from the image data including defects are large at positions where defects exist. Therefore, it is possible to judge that the address has the defects.
However, according to a recent trend, an aluminum film and so on are formed by sputtering, wherein a grain boundary with harsh roughness, called a grain, is formed on a surface of the film to reduce an illumination reflectance at this portion. Therefore, a pixel signal difference from the defect such as a hiatus of conductive pattern is decreased, whereby it becomes difficult to judge whether the pattern is normal or defective. Thus, there are cases that inspection equipments do not properly function.
A specific example of the cases will be described in reference of figures. FIG. 14a through 14d illustrate a specific example of the conventional inspection method. FIG. 14a illustrates an example of reference image data stored in the pick-up image memory 32 in an image area A, and FIG. 14c illustrates a pixel signal at a position R. FIG. 14b illustrates an inspection image data including defects, picked up from the image area A, and FIG. 14d illustrates a pixel signal at a position E corresponding to the position R, and a differential pixel signal between the position E and position R. In FIG. 14a, numerical reference 34a designates a conductor pattern without roughness, and numerical reference 38 designates an oxide film, of which pixel signals are, for example, about 80 and about 25 as in FIG. 14c. In FIG. 14b, numerical reference 34a designates a conductor pattern without roughness; numerical reference 34b designates a roughened portion, in which grains are formed; numerical reference 38 designates an oxide film; numerical reference 35 designates a short-circuit of the conductor; numerical reference 36 designates a hiatus of the conductor; numerical reference 37 designates a deposited conductive extraneous matter, of which pixel signals respectively are about 80, 35, 25, 80, 25, and 60 as in FIG. 14d. In FIG. 14d, a result of an operation of a differential pixel signal between the inspection image data in FIG. 14b and the reference image data in FIG. 14a is shown. For example, when a threshold value for judging defect is set to be 15 to judge whether or not an absolute value of the differential pixel signal exceeds the threshold value, the grain 34b, being a normal conductor pattern, is also judged defective because values corresponding to the short-circuit, the hiatus, and the conductive extraneous matter exceed the threshold value, and an absolute value of the differential pixel signal corresponding to the grain 34b exceeds the threshold value.
Further, also in a case that a conductor pattern is deliberately formed so as to be roughened in order to increase a surface area of a roughened surface capacitor, an illumination reflectance is decreased, whereby there is a problem that a normal pattern cannot be recognized. Also in this case, there are a drawbacks that a normal device is scraped judged defective and scrapped because a normal portion is judged defective or that a failure should be further judged by an inspection using an electric pixel signal after entire processes without inspecting in processes for film formation, etching, and so on. Further, when process conditions, such as a temperature and a gas quantity, are newly studied, it is impossible to evaluate a defect incidence by a visual inspection in the processes.